curl / libcurl / API / curl_easy_setopt / CURLOPT_DNS_CACHE_TIMEOUT

CURLOPT_DNS_CACHE_TIMEOUT explained

Name

CURLOPT_DNS_CACHE_TIMEOUT - life-time for DNS cache entries

Synopsis

#include <curl/curl.h>
 
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_DNS_CACHE_TIMEOUT, long age);

Description

Pass a long, this sets the timeout in seconds. Name resolves will be kept in memory and used for this number of seconds. Set to zero to completely disable caching, or set to -1 to make the cached entries remain forever. By default, libcurl caches this info for 60 seconds.

The name resolve functions of various libc implementations do not re-read name server information unless explicitly told so (for example, by calling res_init(3)). This may cause libcurl to keep using the older server even if DHCP has updated the server info, and this may look like a DNS cache issue to the casual libcurl-app user.

Note that DNS entries have a "TTL" property but libcurl does not use that. This DNS cache timeout is entirely speculative that a name will resolve to the same address for a certain small amount of time into the future.

Default

Protocols

All

Example

CURL *curl = curl_easy_init();
if(curl) {
  curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/foo.bin");
 
  /* only reuse addresses for a short time */
  curl_easy_setopt(curl, CURLOPT_DNS_CACHE_TIMEOUT, 2L);
 
  ret = curl_easy_perform(curl);
 
  /* in this second request, the cache will not be used if more than
     two seconds have passed since the previous name resolve */
  ret = curl_easy_perform(curl);
 
  curl_easy_cleanup(curl);
}

Availability

Always

Return value

Returns CURLE_OK